Technical Abstract:
For the last four years, scientists at the USDA, Agricultural Research Service, Northern Plains Agricultural Research Laboratory have been searching for alternative soil and crop management practices to reduce greenhouse gas emissions and increase carbon and nitrogen sequestration.
“If we can reduce greenhouse gas emissions and increase carbon sequestration by using alternative management practices, we can reduce global warming, improve soil and environmental quality, and sustain crop yields,” says Research Soil Scientist Upendra M. Sainju, Ph.D., lead researcher on the project.
Currently 20 to 25 percent of greenhouse gases come from agriculture, but Upendra hopes his research will lead the way for farmers to change their farming practices. He uses two experimental research plots in Rasmussen, eastern Montana and Nesson Valley, North Dakota in which he tests four management practices: 1) use no-tillage (no cultivation) and grow barley continuously each year, 2) use no-tillage and rotate barley and pea crops each year, 3) use no-tillage and switch barley and fallow (letting the soil rest without crop) each year, and 4) use conventional tillage and switch barley and fallow each year. All treatments are applied with or without nitrogen fertilizer to barley.
He uses three criteria to determine which is the best practice: 1) reduce greenhouse gas emission, 2) improve soil quality through carbon and nitrogen sequestration (taking carbon dioxide from the air by plants and putting it back into the soil as well as reduce N losses through leaching and volatilization), and 3) maintain crop yields.
For the first criteria, “What we've found is that when you use the no-tillage practice, it reduces carbon dioxide emission because no-tillage does not disturb soil,” Upendra said. When soil is mixed by cultivation, microorganisms within the soil become active, which release carbon dioxide into the air by decomposing soil organic matter. No-tillage can generate additional income by increasing carbon sequestration through carbon trading.
Tillage and alternate-year fallow cause soil to lose its nitrogen by up to five times more, mostly by leaching, as compared to no-tillage and annual cropping. By losing nitrogen, farmers must use more fertilizer to maintain crop yields, which can be costly. The fallow system was found to be the worst practice (but the most used by farmers) because there is less crop residue returned to the soil to maintain its quality, which ultimately helps in increasing crop yields.
Upendra found that using no-tillage with barley and pea rotation each year meets all three criteria. Peas don't need nitrogen because they fix nitrogen from the atmosphere. That means no extra work and money saved. When the time comes to switch crops during the planting season, nitrogen supplied by pea residues reduces the amount of nitrogen fertilizer for succeeding barley. Further, it produces a good crop yield.
Upendra's results revealed that on a yearly average, carbon dioxide emissions were reduced by about 10 percent when using barley-pea rotation compared with continuous barely. This is because barely yields more than pea and also increases carbon dioxide emission through increased root respiration (breathing from roots). Now USDA is working to get the information out to farmers. “We have a focus group here where we invite producers for a meeting two times a year and at the meeting we present our research data,” Upendra said. “We also publish our results in journals and bulletins and disseminate them in field tours and agricultural fairs. They are getting the information. It's just that it's kind of slow.”
One of the problems researchers have found is the expense of using no-tillage. The initial cost for purchasing the no-tillage equipment can run thousands of dollars. “So unless the government subsidizes that kind of expenses or provide incentives to use the equipment...it is hard to convince farmers to switch the system,” he said.
“Carbon dioxide is only one of the three greenhouse gases emitted from croplands. The other two are nitrous oxide and methane”, Upendra says. “The present four-year study deals with carbon dioxide emission and carbon sequestration. Further studies are going on to evaluate the effects of alternative farming practices on nitrous oxide and methane emissions and on long-term studies to account for the year-to-year variability on all three greenhouse gas emissions and carbon and nitrogen sequestration”.
Upendra expects President Barak Obama and Legislatures to come up with some kind of legislation that would help farmers to begin the transformation. “I think President Obama is going to introduce the climate change legislation where producers can generate extra income by increasing carbon sequestration through carbon trading and reducing greenhouse gas emissions that improve environmental quality and reduce global warming by using alternative agricultural management practices, such as no-tillage with continuous cropping or crop rotation, instead of using conventional tillage with the crop-fallow system.